1. Field of Invention
The present invention relates to a voltage controlled oscillator. More particularly, the present invention relates to a voltage controlled oscillator employing XOR logic unit, and electronic system using the same.
2. Description of Related Art
The construction of a conventional voltage controlled oscillator is explained referring to FIG. 1. Generally, a voltage control oscillator (VCO) 10 has a plurality of inverters 100, 102 and 104, which are connected in series, a plurality of resistors 110, 112, 114 and 116, and a capacitor 120. A supply voltage VDD (which is not shown) applied to the inverters 100, 102 and 104 makes the inverters 100, 102 and 104 output signals in response to voltage inputs to respective inverters, wherein the respective output signals are either input to downstream inverters or output of the VCO 10 as the case may be.
However, the conventional voltage control oscillator 10 has the following problems. The maximum frequency output from the VCO can only be obtained when the input voltage equals to VDD/2. Therefore, the output range of the frequency is limited. Further, many passive units are required to be used and these passive units together determine the maximum frequency.